Can someone please share the typical cost of material to 3D print an object like a raspberry pi case? Thank you.
This depends on what you mean by "cost". If you've got your own (or access to a) 3D printer and you're just paying for raw material then you can calculate the raw material cost per cubic distance (cubic inches, cubic centimeter, whatever your preferred units are), then determine the volume of the part to be printed, then multiply the two together.
Typically the CAD software used to create the 3D model will have a button that gives you the volume of the part.
Sometimes, as in selective laser sintering (SLS), the high temperatures involved degrade the unused nylon powder. This means that some percentage of the powder needs to be exchanged after some number of builds, and you'll wind up paying a higher cost than strictly the cost per unit volume of the powder (to pay for the replacement of the unused powder).
If you don't have access to the printer, then you'll wind up paying the same costs mentioned above, plus whatever their going rate is for time on the machine, time to setup the part, time to inspect/depowder/clean the part, shipping, and markup.
If you're interested in getting someone else to 3D print the part (and give you an instant quote), try a site like Shapeways.